1. Field
This disclosure relates generally to semiconductors, and more specifically, to the radio frequency power devices.
2. Related Art
In the field of wireless communication, integrated circuits commonly implement radio frequency power amplifiers (RFPAs) which supply an amplified amount of output power. The operating frequencies for wireless communication have increased as the demand for wireless communication has increased. RF power amplifiers must have sufficient gain and bandwidth for operation well into the gigahertz range. Conventional RF power amplifiers have an upper limit to the bandwidth of the input signal that can be amplified before incurring excessive distortion and ruggedness issues. As signal bandwidth is increased, conventional RF power amplifiers exhibit increased distortion in the sidebands. Additionally, high voltage excursions are present on the drain electrode of the power transistor used for amplification. The bandwidth limitation imposed on RF power amplifiers is caused by several sources. One source of the bandwidth limitation is due to impedance resonances loading the gate and drain of the power transistor. The interaction between components which are internal to the pre-matched RF power transistor and external circuit board components creates resonances at frequencies that are of the order of the modulation bandwidth of the RF signal.
Another aspect of RF power amplifier operation is the use of Digital Pre-Distortion (DPD). Digital Pre-Distortion is a system which is used in conjunction with RF power amplifiers to reduce the level of distortion and thereby comply with linearity specifications. Conventional DPD systems perform well for RF power amplifiers up to signal bandwidths where the baseband impedance is low and the phase is close to linear. However, any kind of resonance or rapid phase transition presents a hard limit for Digital Pre-Distortion correction.
Another behavior of RF power amplifiers is the presence of a low frequency gain peak which is attributable to the pre-matched RF power transistor. This gain peak is out-of-band but it is important that the peak be as low as possible. The low frequency gain peak can cause stability issues, as well as linearization problems when using a DPD system. Conventional RF power amplifiers generally do not have all of the characteristics of very high signal bandwidth, low RF power transistor drain voltage swing, good digital pre-distortion correction and low out of band gain peaks.